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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 63 (1977), No. 8

  • Analysis of CO Reduction of Hematite Pellets by Malti-interface Model

    pp. 1229-1234

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    Reduction experiments of hematite pellets with CO or CO-CO2 gas mixtures were carried out under Various experimental conditions. The hematite pellets were made of pyrite cinder and the porosity was approximately 13%.
    Observed reduction curves were simulated by the multi-interface model where rate parameters obtained by the technique of step-wise reduction of the pellets were used. Agreement between the calculated curves and observed data was satisfactory for the wide variety of experimental conditions as to reduction temperature (800-1000°C), gas composition (p (b) CO=0.47-1.0atm), gas flow rate (Q=0.5-3.6Nl/min), and pellet radius (r0=0.52-0.78cm).
  • Hydrogen Contents of Slag and Ingot in ESR Process

    pp. 1235-1243

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    ESR experiment was made to determine the value of hydrogen distribution between slag and metal, and to clarify operational factors intfluencing the hydrogen content of ingot at a steady state. Compositions of electro-slags used were CaF2-25%Al2O3, CaF2-25%CaO, CaF2-25%CaO-25%Al2O3, CaF2-30%CaO-20%SiO2, and CaF2-30%CaO-10%SiO2-10%Al2O3. Steels of SUS 304 type and S45C type (0.45% carbon steel) were remelted at 200g/min under the water vapour pressure ranging from 1 to 16 Torr.
    The experimental result showed that the ratio of the hydrogen content of slag to that of ingot was kept at a constant value during ESR, irrespective of the hydrogen content of electrode and the water vapour pressure. Accordingly, the observed ratio was concluded to be fully close to the equilibrium concentration ratio.
    The hydrogen content of ingot at a steady state was found to be expressed as a linear function of two variables: the square root of the water vapour pressure and the hydrogen content of electrode.
    This observed linear function was proved to be consistent with an equation derived from a material balance consideration of hydrogen in slag. On the basis of this consistency, the water solubility in slag was evaluated and its dependence on slag composition was discussed.
  • Desulphurization of Ferritic Stainless Steel by Hydrogen-Argon

    pp. 1244-1251

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    Desulphurization of molten ferritic stainless steel (25%Cr-Fe alloy) was studied by using plasma jet of hydrogen-argon gas mixture to which powders of various calcium bearing fluxes were supplied.
    The fluxes used were (6-17) wt%CaC2-CaF2, 20wt%CaO-CaF2 and 12wt%CaC2-(18-35) wt%CaO-CaF2, the diameters of powder particles were smaller than 149μm, and the powder feeding rates were 0.1 to 0.9g/min. The results were summarized as follows: 1) the desulphurization efficiency of CaC2 in CaC2-CaF2 was 30-40%, and the minimum sulphur concentrations attained were as low as 0.0007% by CaO-CaF2 and 0.0013% by CaC2-CaF2, 2) hydrogen in the plasma, which reacted with CaC2 to form hydro-carbon gases, effectively enhanced desulphurization, preventing the carburization from CaC2, but retarded the desulphurization above pH2=0.5atm by forming gaseous calcium, 3) the present results together with those in the previous work indicated the possibility of the refining of ferritic stainless steel with very low levels of carbon, nitrogen and sulphur by hydrogenargon plasma jet using CaC2-CaF2 or CaO-CaF2 flux.
  • Mineralogical Study of LD Converter Slags

    pp. 1252-1259

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    Mineralogical study of LD converter slags was carried out by means of microscopic, EPMA and X-ray examinations and three crystalline phases, namely (i) dicalcium silicate (ii) dicalcium ferrite (iii) spinel phase or ‘FeO’ solid solution were identified. Phosphorus was found to exist only in the solid solution of 2CaO·SiO2. The rapidly and slowly cooled synthetic slags of CaO-SiO2-FeOx system containing 5wt% P2O5 were also studied by the same method. The slag compositions with different primary phase area chosen in order to obseve the phosphorus-enriched phase. The results of the CaO-SiO2-Fe2O3 system indicate that silico-carnotite [5CaO·SiO2·P2O5] was formed and it changed to the fluorapatite [Ca5F (PO4) 3] when 5 wt% of CaF2 was added. On the other hand, in the system CaO-SiO2-‘FeO’, silico-carnotite was formed only in the Ca2SiO4 primary phase area.
  • On Defects Originated from the Center Porosity of the Continuously Cast Blooms

    pp. 1260-1268

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    The defects originated from center porosity of the continuously cast blooms have been revealed by the study on the unusual tesile fractures of the PC steel wires which contain B and Ti. The cracks initiated at the tesile fractures are caused by the nonmetallic inclusions at the center porosity of blooms during the heating in the soaking pit for the billeting.
    The degree of the oxidation depends upon the center porosity and heating condition. The marked oxidation of blooms containing B and Ti is caused by the development of columnar dendrites and the increase of center porosities. The oxidation of the center porosity at the ends of bloom can be prevented by controlling the casting temperature and improving the solidification structure of the bloom.
  • On the “Pattern” Occuring in the Outer Part of the Continuously Cast Al-Si Killed Steel Blooms

    pp. 1269-1278

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    In the circum ferential part of continuously cast blooms, there is a zone of more intensive colouration in macro-etching than parts of the cross-section. This zone is called the “pattern”. In order to make clear the formation mechanism of the “pattern”, the casting structure and distribution of sulfide inclusions are investigated.
    The results obtained are as follows:
    (1) The “pattern” is obseved more clearly in Al-Si killed steel than in Si killed steel.
    (2) In the “pattern”, sulfide structures are very fine and the ratio of interdendritic area is higher than other parts.
    (3) In the “pattern”, sulfide inclusions precipitated at the interdendritic area are very fine and numerous.
    (4) When the upward-streaming type immersion nozzle is used, the solidification rate in the lower part of the mold in the bloom caster is higher than that in the spray zone. It is concluded that the “pattern” of the continuously cast bloom is formed in the rapid solidification zone in the mold.
    (5) The reason why Al-Si killed steel exhibits the “pattern” more clearly is explained by the role of Al2O3 as nucleation sites for solidification.
    (6) Any difference in mechanical properties between the “pattern” and other parts is not observed.
  • On the Behavior of Al2O3 Clusters during the Solidification of Continuously Cast Slabs

    pp. 1279-1286

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    In the slabs of Al-Si killed steel cast continuously by the vertical-type caster, some Al2O3 clusters accumulate below the slab surface. By investigation on the macro-and micro-structures of slabs, it was clarified that the Al2O3 clusters were entrapped when the columnar dendrite grew discontinuously.
    This discontinuity has been improved by the control of the casting temperature. Then, the defect originated from the non-metallic inclusions at welds of ERW pipe, especially that with large thickness and small diameter, has been reduced.
  • Quality Improvement of Continuously Cast Stainless Steel Blooms through Electromagnetic Stirring

    pp. 1287-1296

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    Electromagnetic stirring was applied in order to improve the qualities of continuously cast stainless steel blooms for seamless tubes.
    The results are summerized as follows:
    (1) Grain refinement of cast structure of blooms is obtained by the stirring. The tendency to the equiaxed crystals grow is stronger in the order SUS 316, SUS 321, SUS 304 and SUS 430.
    (2) White bands, negative segregation bands of solutes, in stirred blooms are formed. Negative segregation of solutes at the white band increases its intensity in proportion to equilibrium partition coefficient of solutes.
    (3) Center cavities in blooms are converted into dispersed pourous form from pipe form and the star cracks disappear by the stirring.
    (4) A homogeneous distribution of δ-ferrite in SUS 304 blooms and a refinement of Ti (CN) clusters in SUS 321 blooms are obtained by the stirring.
  • Elastoplastic Stress Analysis of Bulging as a Major Cause of Internal Cracks in Continuously Cast Slabs

    pp. 1297-1304

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    A theoretical calculation has been made of bulging as a major cause of internal cracks arising in the secondary cooling zone in strand cast slabs. Temperature distribution in the solidifying shell has preliminarily been determined from a heat transfer model, then an elastoplastic stress analysis of the shell has been made in terms of the finite element method.
    A quantitative evaluation of the influence on bulging has been carried out of the withdrawal rate, spray water flux, pitch between rolls and disorder in the alignment of rolls, leading to an effective means to prevent bulging under high withdrawing rate condition. Factors influencing the critical bulging strain beyond which internal cracks develop are also discussed.
  • Role of Recrystallization and Austenite Formation in Forming (α+γ) Microduplex Structures in Cold Rolled Martensitic Fe-10Ni Alloys

    pp. 1305-1311

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    For the purpose of finding practical means to obtain ultrafine grain structures, competition between the recrystallization of martensite and the formation of austenite was studied during annealing of cold worked Fe-Ni martensitic alloys in the (α+γ) field.
    In an Fe-10%Ni alloy a “microduplex structure” was formed above a critical temperature where the formation of austenite advanced prior to the recrystallization of martensite. Below the temperature the recrystallzation preceded the austenite formation, resulting in a “recrystallized ferrite structure”.
    Addition of 0.18%Nb and 0.02%C to the alloy caused marked retardation of recovery and recrystallization of deformed martensite with little effect on the austenite formation. Consequently, an increment of the recrystallized ferrite fraction compared to a given amount of transformed austenite during annealing in the (α+γ) region is reduced to one fifth and the “microduplex structure” can be obtained by annealing at lower temperatures.
  • The Effect of Sub-critical Quenching on Fatigue Limits for Crack Initiation and for Failure of Press-fitted Part in Axle

    pp. 1312-1320

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    To improve the fatigue limits of press-fitted parts of axles by sub-critical quenching, that is, water quenching from the temperature just below Ac1 point, the effects of the heat treatment conditions on microstructure, hardness, residual stress distribution, rotating bending fatigue limits for crack initiation, σw1, and that for failure, σw2 were examined. Steels used for the experiment were normalized 0.35-0.45 %C steels for machine structual uses. For fatigue testing, press-fitted specimens of 50mm in diameter were mainly used.
    (1) The microstructure of specimen was hardly changed by sub-critical quenching, but the surface hardness was slightly increased.
    (2) High residual compressive stress, distributed from the surface to considerable depth of the core, was detected in sub-critical quenching specimens.
    (3) σw1 and σw2 of press-fitted specimens were both improved considerably by sub-critical quenching. Moreover, the limit depth of non-propagating crack, measured after the fatigue test in which applied stress was just below σw2, was also remarkably increased.
    (4) It was supposed that σw1 of the press-fitted specimen could be improved by the increase of surface hardness, and σw2 by the increase of residual compressive stress in surface zone, respectively.
  • Static Tensile Properties of Mixed Structure of Martensite and Residual Ferrite in Ni-Cr-Mo Steels Containing Low Carbon

    pp. 1321-1330

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    A study has been made of static tensile properties of mixed structure of martensite and residual ferrite in Ni-Cr-Mo steels containing low carbon. Results obtained are as follows:
    (1) Both of the strength and ductility were approximately specified by volume fraction of residual ferrite.
    (2) The 0.2% proof stress gradually deviated from the law of mixture with an increase in residual ferrite at 200°C temper, but approximately followed it at 600°C temper.
    (3) Reduction in area gradually decreased at 200°C temper, but somewhat increased at 600°C temper with an increase in residual ferrite.
    (4) From the analyses of true stress-true strain diagrams and microfractographs, it is considered that residual ferrite, when it appeared in lower tempered martensite, has a detrimental effect on ductility, because the residual ferrite in a low fraction fractures in a brittle manner due to plastic restraining of it by surrounding martensite matrix in the process of plastic deformation, and that with increasing in the residual ferrite both of the martensite matrix which become to be more brittle and the residual ferrite fracture in a brittle menner.
  • Tensile Properties of High Cr-Fe Alloys with Small Amounts of C and N, Annealed at High Temperatures

    pp. 1331-1339

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    Tensile properties of high Cr-Fe alloys with small amounts of C and N were investigated after the heat-treatments in the temperature range from 800 to 1200°C followed by air cooling (A.C.) or water quenching (W.Q.). The yield strength, σy, and the tensile strength, σB, showed considerable scattering with heat treatments even when the same condition of annealing was used.
    However, Δσy defined as the difference between σy of A.G. specimens and σy of W.Q. ones where those specimens were heated at a time in a furnace, was uniquely determined by the annealing temperature. Δσy was primarily explained by the difference between the Ky·d-1/2 term of Hall-Petch eq. for A.C. specimens and that for W.Q. ones, but some part of Δσy explained by the difference in the friction term, was present. Small difference in contents of C and N significantly affected the responces of ductility and of grain size in these alloys to the change in annealing temperature.
  • Flow Stress at Low Temperatures and Strain Aging of High Cr-Fe Alloys with Small Amounts of C and N

    pp. 1340-1349

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    Mechanical properties and aging responses of 1mm thick plate specimens of 24-26% Cr-Fe alloys with small amounts of C and N were studied in the temperature range from-196 to 200°C.
    The thermal components of the flow stress at low temperatures (<-20°C) were found to be independent of the heat treatments employed for the specimen preparation. However, in the specimens solution treated above 1200°C and subsequently quenched, the sotid solution hardening due to interstitial atoms was identified to contribute significantly to the flow stress increases at higher temperatures. The air cooled and the aged (1h at 400°C) specimens were identical in the yield stress and the tensile strength, while they were different in the Luders elongation. Some of strain aging characteristics of the aging at 200°C were similar to those of the aging of the pure iron. Water quenched specimens showed the highest low-temperature ductility.
  • Diffusion in Liquid Iron and Its Alloys

    pp. 1350-1361

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  • 1976 IIW Annual Assembly

    pp. 1362-1364

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  • 抄録

    pp. 1365-1373

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